The present invention relates to a process for the treatment of basic aqueous effluents containing plutonium and possibly uranium, which can in particular be used for treating aqueous effluents obtained by the alkaline washing of organic solvents used in installations for the reprocessing of irradiated nuclear fuels.
In installations for the reprocessing of irradiated nuclear fuels, organic solvents are normally used for extracting the plutonium and uranium from nitric solutions for dissolving the irradiated fuels. Following this extraction stage in the organic solvent, the uranium and plutonium are recovered by selective re-extraction in aqueous solutions. The organic solvent is then treated to purify and decontaminate it before recycling it in the uranium and plutonium extraction stage.
In general, the purification treatment of the solvent comprises an alkaline washing stage performed, for example, by means of a sodium carbonate solution. When the solvent is tributyl phosphate, the alkaline washing stage using a sodium carbonate solution makes it possible, on the one hand, to extract in the aqueous solution, dibutyl phosphoric acid [(DBP.sup.- H.sup.+)], which is the main degradation product of tributyl phosphate and, on the other hand, maintain in aqueous solution the heavy metal ions and in particular uranium, zirconium and especially plutonium, due to the complexing properties of the carbonate ion.
Thus, at the end of the alkaline washing stage, radioactive effluents are obtained, which contain in solution traces of plutonium and uranium. In order to ensure the subsequent treatment of these radioactive effluents, under good conditions, it is preferable to concentrate them by evaporation in order to in this way reduce the volume of effluents to be treated.
However, concentration by evaporation at atmospheric pressure of effluents of this type suffers from a major disadvantage. During evaporation, there is a partial, but relatively large precipitation (approx. 50%) of the plutonium which was initially in solution, which is rather hazardous due to the possibility of an accumulation of a critical amount of plutonium both in the evaporator and in the means for the storage and transportation of the concentrated effluents.